Electric discharge device



Dec. 7, 1965 D. s. GUSTIN 3,222,556

ELECTRIC DISCHARGE DEVICE Filed April 17, 1962 DANIEL S. GUSTININVENTOR.

ATTORNEY United States Patent 3,222,556 ELECTRHC DTSQHARGE DEVHCE DanielS. Gustin, ilondonderry, N.H., assiguor to Sylvania Electric Productsline, a corporation of Delaware Filed Apr. 17, 1962, Ser. No. li8,091 5Claims. (Cl. 313-25) This invention relates to high pressure, electricdischarge devices for use in constant current series circuits.

High pressure electric discharge devices, commonly known as mercuryvapor lamps or merely mercury lamps, are Well known to the art and suchdevices have previously been used in constant current series circuits.These devices include an inner arc tube which encloses a mercurydischarge during lamp operation. The are tube is generally supportedwithin an outer bulbous envelope by a metallic frame or harness. At oneend of the arc tube a starting probe is located in close proximity to amain discharge electrode and another electrode is located at theopposite end. A filling of argon gas and a drop of mercury are enclosedwithin the tube.

When the lamp is turned on, full starting voltage is applied between thestarting probe and electrode near it. The voltage causes a glowdischarge of argon gas between these members and gradually, the heat ofthe discharge vaporizes some of the liquid mercury in the tube. As thevaporization continues, pressure builds up and mercury ions are formedunder the influence of the electrode discharge. When sufiicientionization occurs, an arc will then strike between the two maindischarge electrodes.

Although the arc in the tube is usually quite stable during a continuingapplication of line voltage, it may fail if an interruption in thecurrent occurs. When such interruptions occur in a constant currentseries circuit, and the arc tube is still warm, often the arc does notrestrike between the electrodes but rather may randomly form betweenvarious elements on the arc tube harness. Formation of an arc upon theharness will cause its destruction.

Even a momentary interruption of a few cycles may cause failure of thearc in the tube. The ionization of the mercury in the tube then ceasesalmost immediately and will not reoccur even with the application ofexcessive voltages if the mercury vapor pressure remains high. However,ionized mercury is essential for the formation of an arc. Only coolingof the tube together with reduction of mercury vapor pressure will allowarc reformation and such cooling can take up to a half hour.

Yet, a constant current transformer which is included in the circuitwill keep attempting to strike an are between the electrodes bydelivering higher and higher voltages irrespective of whether themercury vapor pressure is high or not. Excecdingly high voltages,possibly as high as 6,000 volts, can be built up in the circuit. Withvoltages this high, an arc may randomly stroke on the arc tube harnesssince an arc is not forming in the arc tube. When such random arcsoccur, the heat generated will gradually melt the harness at the pointof discharge and may eventually destroy the lamp.

Not withstanding the fact that this problem occurs in a constant currentseries circuit, such circuitry is quite commonly used in street lightingwith mercury lamps. Probably the main reason for the prevalency of suchcircuitry is that before the advent of mercury vapor lamps for streetlighting, and possibly even before the customary use of incandescentlamps, carbon arcs were frequently used. The industry had found that itwas easy to combine carbon arcs into series circuits and wiring costswere materially reduced. Rather than doubling wiring costs by usingparallel circuitry, it was substantially more economical to extend asingle wire loop from a power station out to the carbon arcs and backagain to the station. Then when mercury vapor lamps were introduced forstreet lighting, they were incorporated into the existing seriescircuits.

Accordingly to my invention, to control random arcing in a constantcurrent series circuit, I place a pair of higl1- melting conductiveannuli within the bulbous envelope upon conductors of differentpotentials. These annuli are placed fairly close to each other so thatany random arcing will preferentially form between them rather thenbetween portions of the harness. Since these conductive annuli are madeof highdnelting materials, even great heat produced by the random arcingwill not melt them and if such arcing occurs, the harness will remainintact. Once the random arc is established, it will continue betweenthese conductors so long as current is maintained in the circuit. Whenthe current is turned off again the random arcing will stop and if thearc tube is then cool, subsequent application of current will producethe formation of a normal are within the tube. Thus, if the currentmomentarily fails during the evening, and the arc in the arc tube fails,a controlled arc can then strike between the conductors and continueuntil the current is turned off, possibly the next morning. Thefollowing evening when the current is again turned on in the circuit, anarc will reform properly within the arc tube.

Accordingly, the primary object of my invention is the prevention ofuncontrolled random arcing on an arc tube harness.

A feature of any invention is the positioning of a pair of high-meltingconductors within the bulbous envelope so that an arc willpreferentially strike between these con ductors when it cannot form inthe tube.

An advantage of any invention is that outage of mercury lamps caused byrandom arcing and destruction of the arc tube harness is reduced.

The many other objects, features and advantages of the instant inventionwill become manifest with those versed in the art upon reading thefollowing specification when taken in conjunction with the accompanyingdrawings, wherein a specific embodiment of this invention is shown anddescribed by way of an illustrative example.

Referring to the figure an elevational view of a mercury vapor lamp isshown. For clarity of presentation, the outer bulbous envelope and thebase for the lamp are shown in phantom lines surrounding the arc tubeharness and the arc tube.

A high pressure mercury vapor lamp such as shown in the drawing,comprises an outer vitreous envelope or acket 2 of generally tubularform having a central bulbous portion 3. The jacket is provided at itslower end with a re-entrant stem it having a press through which extendsrelatively stiff lead-in wires 6 and 7 connected at their outer ends tothe electrical contacts of a usual screwtype base 8 and at their innerends to the arc tube and the harness.

The are tube 12 is made of quartz and has sealed therein at oppositeends, the main discharge electrodes 13 and 14, which are supported onlead-in wires 4 and 5 respectively. Each main electrode comprises a coreportion which may be a prolongation of the lead-in wires 4 and 5 and maybe prepared of a suitable refractory metal such as tungsten ormolybdenum. The prolongations of the lead-in wires 4 and 5 aresurrounded by tungsten wire helixes. A small elongated piece or sliverof thorium metal (not shown) is inserted between the core and the helixto reduce the cathode drop during operation. An auxiliary starting probeor electrode 18 is provided at the base end of the arc tube 12 adjacentmain electrode 14 and comprises an inwardly projecting end of anotherlead-in wire.

Each of the current lead-in wires described above have their ends weldedto intermediate foil sections of molybdenum which are hermeticallysealed within pinch seal portions of the quartz arc tube. The foilsections are very thin, for example, approximately 0.0008 thick and gointo tension without rupturing or scaling off when the quartz cools.Relatively short molybdenum wires 23, 24- and 35 are welded to the outerends of the foil and serve to convey current to the various electrodesinside the arc tube 123.

Metal foil strips 45 and 46 are welded to the outer ends of the lead-inwires 23 and 24 respectively. A resistor 26 is welded to foil strip 45which in turn, is welded to the arc tube harness. The resistor may havea value of, for example, 40,000 ohms and serves to limit current toauxiliary electrode 18 during normal starting of the lamp. Metal foilstrip 4-6 is Welded directly to stiff lead-in Wire 7. Lead-in wire 35 iswelded at one end to a piece of molybdenum foil sealed in the arc tube12 which in turn is welded to main electrode 13. Metal foil strip 4-7 iswelded at one end to lead-in wire 35 and at the other end to theharness. The pinched or flattened end portions of the arc tube 12 form awide seal using substantially the full diameter of the tub-e 12 and aremade by flattening or compressing the ends of the arc tube 12 While itis heated. The are tube 12 is provided with a filling of an ionizablemedia such as mercury in sufficient quantity to be completely vaporizedwhen pressure is developed in the order of A2 to several atmospheresduring operation of the lamp. In addition, a small quantity of a raregas such as argon, at a normal pressure of 25 mm. of mercury isintroduced to facilitate starting.

The U-shaped wire, internal supporting assembly or arc tube harnessserves to maintain the position of the are tube 12 substantially coaxialwithin the envelope 2. To support the arc tube 12 within the envelope 2,the stiff lead-in wire 6 is welded to the base 53 of the harness.Because stiff lead-in wires 6 and '7 are maintained at differentelectrical potentials, they must be insulated from each other, togetherwith all members electrically associated with each of them. Clamps 56and 57 which hold the arc tube 12 at the pinched end portions arefixedly attached to legs 54 of the harness and thus support the arc tube12 within the outer envelope 2. A rod 59 bridges the free ends of theU-shaped support wire 54- and is fixedly attached thereto to impartstability to the structure. The free ends of the U-shaped support wire54 are also provided with a pair of resilient metal leaf springs 60,frictionally engaging the upper tubular portion of the lamp envelope 2.A heat shield 61 is positioned beneath the arc tube 12 and above theresistor 26 so as to protect the resistor from excessive heat generatedduring lamp operation.

Conductive annuli 30 and 31 are preferably disposed upon stiff lead-inwire 6 and '7 respectively. Each of these conductive annuli 6 and '7 arespaced from each other so as to form a gap across which an arc can formif it can not form in the arc tube 12. Ordinarily the random arcs wouldform between the sharpest points available in a device and in mercurylamps this would be between the end 27 of the wire leading to theresistor 26 and stiff lead-in line '7. Of course, the conductive annuli30 and 31 must be in a conductive relationship with the members on whichthey are disposed.

In normal operation of the lamp, the stiff lead-in wire 6 serves as onesource of potential and the lead-in wire '7 serves for the other. Sincebase 53 of the U-shaped harness is welded to stiff lead-in wire 6, theharness, together with members electrically connected with it, becomepart of the circuit. Thus, starter probe 18 and main electrode 3 areconnected to one side of a power line in the circuit and main electrode14 is connected to the other side of the line. Lead-in wire 7 thus notonly must be electrically insulated from lead-in wire 6, it must beinsulated from the rest of the harness to prevent shortcircuiting.Insulating tubes, 33 and 34 surrounding foil strips 45 and 46,respectively, insure insulation of the 4 strips from each other and alsoof strip 45 from the harness and heat shield 61.

Many materials may be used for the conductive annuli and although Iprefer to use compacted graphite because: of its economy, tantalum,zirconium, tungsten, vanadium or molybdenum and the carbides of each ofthese several metals may also be used. I prefer to use aconductiveannulus with a round peripheral shape, however other shapessuch as squares or triangles are also very readily adapted to thestructure. Round is preferred however, because even if the annulus movesupon its support a constant gap distance is maintained.

The gap between the conductive annuli 30 and 31 is quite important andthese members must be spaced sufficiently apart so that an arc will notform during nor mal starting or operation of the lamp but will onlystrike upon malfunction of the circuit. However the gap distance willvary depending upon the normal starting voltage of the lamp and themetal or metal compound used for the conductive annulus. These distancescan be readily determined by routine experimentation and for a graphiteannulus I prefer to have a gap of about The diameter of the conductiveannuli together with the thickness is not critical so long as therequisite arc gap is maintained. Although, of course, the thickness mustbe sufficient so that each annulus is self-supporting and the diametershould not be so large that fitting into the outer bulbous envelope isdifficult.

Although we have shown the conductive annuli disposed upon the stiffleadin wires 6 and 7, it is apparent that they may be placed elsewhereon the lamp harness so long as they are on members connected to oppositesides of a power line and if the arc gap is maintained. For example, aconductive annulus may be fitted upon the support frame 53 and anotherupon the stiff leadin wire 7 or the metal strip 46 which is weldedthereto. It is apparent that other modifications may be made in theinstant invention without departing from the spirit and scope thereof.Thus, it is my intention only to be limited by the scope of the appendedclaims.

As my invention I claim:

l. A high pressure electric discharge device comprising: an outerbulbous envelope; a first and a second stiff lead-in wire disposed atthe base of said envelope, each of said lead-in wires being adapted toconduct current from opposite sides of a power line; a metallic harnessdisposed in said envelope and supported upon said first stiff lead-inwire; an arc tube supported upon said metallic harness; electrodesdisposed at either end of said arc tube, one of said electrodes beingelectrically connected to said harness and the other of said electrodeselectrically connected to said second stiff lead-in wire; conductivemeans disposed within said envelope and upon each of said lead-in wiresfor preferentially forming an arc therebetween when an arc cannot strikebetween said electrodes in said are tube.

2. In a high pressure electric discharge device comprising an outerbulbous envelope; a first and a second stiff lead-in wire disposed atthe base of said envelope, each of said stiff lead-in wires beingadapted to conduct current from opposite sides of a power line; ametallic harness disposed within said envelope and supported upon saidfirst stiff lead-in wire; an arc tube supported u on said metallicharness; electrodes disposed at either end of said are tube, one of saidelectrodes being electrically connected to said harness and the other ofsaid electrodes being electrically connected to said second stifflead-in wire; conductive means disposed upon each of said first andsecond stiff lead-in wires for preferentially forming an are when an arccannot strike between said electrodes in said are tube.

3. In a high pressure electric discharge device comprising an outerbulbous envelope; a first and a second stiff lead-in wire disposed atthe base of said envelope, each of said lead-in wires being adapted toconduct current from opposite sides of a power line; a metallic harnessdisposed within said envelope and supported upon said first stifflead-in wire; an arc tube supported upon said metallic harness;electrodes disposed at either end of said arc tube, one of saidelectrodes being electrically connected to said harness and the other ofsaid electrodes being electrically connected to said second stitf leadin wire; a pair of conductive annuli disposed within said envelope andupon each of the conductors from opposite sides of said power line forpreferentially forming an arc therebetween when an arc cannot strikebetween said electrodes in said arc tube.

4. In a high-pressure electric discharge device comprising; an outerbulbous envelope, a first and a second stiif lead-in wire disposed atthe base of said envelope, said lead-in wires being adapted to conductcurrent from opposite sides of a power line; a metallic harness disposedwithin said envelope and supported upon said first stiff lead-in wire;an arc tube supported upon said metallic harness; electrodes disposed ateither end of said are tube, one of said electrodes being electricallyconnected to said harness and the other of said electrodes beingelectrically connected to said second stiff lead-in wire; a firstconductive annulus disposed upon said first stiff leadin Wire and asecond conductive annulus disposed upon said second stifr lead-in Wire,the conductive annuli being spaced from each other for preferentiallyforming an arc therebetween when an arc cannot strike between saidelectrodes in said arc tube.

5. The device according to claim 4 wherein the conductive annuli areformed of graphite.

References Cited by the Examiner UNITED STATES PATENTS 2,677,068 4/1954Martt a- 313-25 DAVID J. GALVIN, Primary Examiner.

1. A HIGH PRESSURE ELECTRIC DISCHARGE DEVICE COMPRISING: AN OUTERBULBOUS ENVELOPE; A FIRST AND A SECOND STIFF LEAD-IN WIRE DISPOSED ATTHE BASE OF SAID ENVELOPE, EACH OF SAID LEAD-IN WIRES BEING ADAPTED TOCONDUCT CURRENT FROM OPPOSITE SIDES OF A POWER LINE; A METALLIC HARNESSDISPOSED IN SAID ENVELOPE AND SUPPORTED UPON SAID FIRST STIFF LEAD-INWIRE; AN ARC TUBE SUPPORTED UPON SAID METALLIC HARNESS; ELECTRODESDISPOSED AT EITHER END OF SAID ARC TUBE, ONE OF SAID ELECTRODES BEINGELECTRICALLY CONNECXTED TO SAID HARNESS AND THE OTHER OF SAID ELECTRODESELECTRICALLY CONNECTED TO SAID SECOND STIFF LEAD-IN WIRE; CONDUC-